U.S. patent number 7,944,954 [Application Number 12/400,788] was granted by the patent office on 2011-05-17 for laser apparatus with all optical-fiber.
This patent grant is currently assigned to Industrial Technology Research Institute. Invention is credited to Hong-Xi Cao, Chien-Ming Huang, Yao-Wun Jhang, Shih-Ting Lin, Hsin-Chia Su, Li-Ting Wang.
United States Patent |
7,944,954 |
Jhang , et al. |
May 17, 2011 |
Laser apparatus with all optical-fiber
Abstract
A laser apparatus with all optical-fiber includes a plurality of
pumping light sources in different wave bands and an optical-fiber
laser system. The optical-fiber laser system includes an optical
fiber at least doped with erbium (Er) element and doped with or not
doped with ytterbium (Yb) element according to a need. The
optical-fiber laser system outputs a laser light through the
pumping light source.
Inventors: |
Jhang; Yao-Wun (Chiayi,
TW), Huang; Chien-Ming (Taipei, TW), Su;
Hsin-Chia (Yunlin County, TW), Lin; Shih-Ting
(Tainan, TW), Wang; Li-Ting (Pingtung County,
TW), Cao; Hong-Xi (Kaohsiung County, TW) |
Assignee: |
Industrial Technology Research
Institute (Hsinchu, TW)
|
Family
ID: |
42284918 |
Appl.
No.: |
12/400,788 |
Filed: |
March 9, 2009 |
Prior Publication Data
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|
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Document
Identifier |
Publication Date |
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US 20100166027 A1 |
Jul 1, 2010 |
|
Foreign Application Priority Data
|
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|
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Dec 31, 2008 [TW] |
|
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97151893 A |
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Current U.S.
Class: |
372/6; 372/71;
359/341.3; 372/69; 359/342; 359/341.1; 359/333; 372/70; 372/68 |
Current CPC
Class: |
H01S
3/0675 (20130101); H01S 3/06791 (20130101); H01S
3/1608 (20130101); H01S 3/094092 (20130101); H01S
3/1618 (20130101); H01S 3/173 (20130101); H01S
3/094096 (20130101) |
Current International
Class: |
H01S
3/30 (20060101) |
Field of
Search: |
;372/6,68,69,70,71
;359/333,341.1,341.3,342 |
References Cited
[Referenced By]
U.S. Patent Documents
Primary Examiner: Harvey; Minsun
Assistant Examiner: Zhang; Yuanda
Attorney, Agent or Firm: Jianq Chyun IP Office
Claims
What is claimed is:
1. A laser apparatus with all optical-fiber, comprising: a
plurality of pumping light sources in different wave bands, wherein
the pumping light sources comprise a first pumping light with a
wavelength in a range from 790 nm to 825 nm, and a second pumping
light with a wavelength in a range from 960 nm to 990 nm, a third
pumping light with a wavelength in a range from 1450 nm to 1550 nm,
and a fourth pumping light with a wavelength in a range from 900 nm
to 930 nm; and an optical-fiber laser system, comprising an optical
fiber at least doped with erbium (Er) element and ytterbium (Yb)
element, wherein the optical-fiber laser system outputs a laser
light of green through the pumping light sources, wherein the
optical-fiber laser system comprises: a combiner, disposed on the
optical fiber to receive the pumping light sources; and a
green-light seed light source, input to the optical fiber also
through the combiner, wherein the optical fiber directly forms a
linear resonance cavity.
2. The laser apparatus with all optical-fiber according to claim 1,
wherein the optical fiber of the optical-fiber laser system is an
annular optical fiber, and the optical-fiber laser system comprises
an isolator and an optical coupler disposed on the annular optical
fiber, and outputs the laser light through the optical coupler.
Description
CROSS-REFERENCE TO RELATED APPLICATION
This application claims the priority benefit of Taiwan application
serial no. 97151893, filed Dec. 31, 2008. The entirety of the
above-mentioned patent application is hereby incorporated by
reference herein and made a part of specification.
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention generally relates to a laser technique, in
particular, to a laser apparatus with all optical-fiber, which is
capable of emitting a green laser light with a high efficiency.
2. Description of Related Art
In recent years, as the laser projection concept has become
prevailing, the demand on green laser light sources with small
scale and high power is gradually increased, but green laser diodes
are still immature. As for diode pumped solid state (DPSS) laser,
the frequency-doubling green laser has problems about assembly
difficulty and heat dissipation, and what's worse, the heat
dissipation further affects the laser stability. As a result, it
cannot achieve both the small scale feature and the desirable heat
dissipation mechanism. However, a green gas laser has problems of
low efficiency, large volume, and high price.
Currently, the realized wave bands of an optical-fiber laser are
mostly close to infrared and middle infrared wave bands, and are
widely applied to mechanical processing, biomedical, and
communicating purposes. However, the optical-fiber laser in
visible-light wave bands is still in the stage of being researched
in the laboratory, and the total power thereof still cannot be
distinctly improved.
In the prior art, in U.S. Pat. No. 5,638,394, a laser diode with a
wavelength of 980 nm serving as a pumping light source emits lights
to an optical fiber doped with both ytterbium (Yb) and terbium
(Tb), and a blue reflecting mirror and a green reflecting mirror
are placed on two ends of the optical fiber, so as to form a laser
resonance cavity. The generated light is not in an all
optical-fiber structure, so the stability thereof is rather poor.
In addition, the optical-fiber laser doped with Tb also has a poor
efficiency. In another U.S. Pat. No. 5,805,631, a laser diode with
a wavelength from 790 nm to 900 nm serving as a pumping light
source emits lights to an optical fiber doped with both
praseodymium (Pr) and Yb, and a laser resonance cavity is formed on
two ends of the optical fiber in a manner of reflecting mirrors or
gratings. A single pumping light source is used, such that the Pr
ion excited state absorption (ESA) effect cannot be sufficiently
utilized.
As for the green lasers, the researching direction thereof is a
laser system with a small size, high power, and high stability.
SUMMARY OF THE INVENTION
Accordingly, the present invention is directed to a laser apparatus
with all optical-fiber.
As embodied and broadly described herein, the present invention
provides a laser apparatus with all optical-fiber, which includes a
plurality of pumping light sources in different wave bands and an
optical-fiber laser system. The optical-fiber laser system includes
an optical fiber at least doped with erbium (Er) element. The
optical-fiber laser system outputs a laser light through the
pumping light source. Furthermore, the optical fiber is doped with
or not doped with ytterbium (Yb) element according to a need.
BRIEF DESCRIPTION OF THE DRAWINGS
The accompanying drawings are included to provide a further
understanding of the invention, and are incorporated in and
constitute a part of this specification. The drawings illustrate
embodiments of the invention and, together with the description,
serve to explain the principles of the invention.
FIG. 1 shows an absorption spectrum of an Er ion according to an
embodiment of the present invention.
FIG. 2 shows a valence electron configuration of an Er ion
according to an embodiment of the present invention.
FIG. 3 is a schematic view of an excitation performed on an Er ion
by a pumping light source of 800 nm according to an embodiment of
the present invention.
FIG. 4 is a schematic view of an excitation performed on an Er ion
by a pumping light source of 970 nm according to an embodiment of
the present invention.
FIG. 5 is a schematic view of an excitation performed on an Er ion
by a pumping light source of 1480 nm according to an embodiment of
the present invention.
FIG. 6 shows an ESA rate of an Er ion according to an embodiment of
the present invention.
FIG. 7 is a schematic view of an energy conversion between Er ions
and Yb ions according to an embodiment of the present
invention.
FIG. 8 is a schematic view of a frequency up-conversion efficiency
simulation by using a Monte Carlo algorithm according to an
embodiment of the present invention.
FIGS. 9-11 are schematic views of a laser system according to
several embodiments of the present invention.
DESCRIPTION OF THE EMBODIMENTS
Reference will now be made in detail to the present embodiments of
the invention, examples of which are illustrated in the
accompanying drawings. Wherever possible, the same reference
numbers are used in the drawings and the description to refer to
the same or like parts.
According to the present invention, in a green light laser system
with a small scale and high power, an optical fiber is doped with
both Er and Yb, so as to improve an absorption efficiency of a
pumping light source and to reduce a quenching effect of Er ions
with a high concentration. In addition, for example, when the
pumping light sources with more than two light sources are applied,
for example, an excited state absorption (ESA) effect of the Er
ions is enhanced, so as to increase an accumulation quantity of the
Er ions in the green light .sup.2H.sub.11/2 energy level effect.
Accordingly, the laser system is further combined with a linear
resonance cavity, an annular resonance cavity, or an amplifier
system, so as to form an all-optical-fiber green light laser with a
high power.
The optical fiber doped with Er ions has a green light laser energy
level with a wavelength from 0.54 .mu.m to 0.55 .mu.m. In the
present invention, the pumping light source with a wavelength of
975 nm, for example, is utilized to excite the Er ions to
accumulate in a meta-stable state .sup.4I.sub.13/2. In addition,
the optical fiber is, for example, an optical fiber doped with both
Er and Yb ions, so that the Yb ions are enabled to absorb the
pumping light source of approximately 975 nm and to be converted to
Er ions, so as to reduce the pump energy wasted by the Er ions due
to the quenching effect. In addition, the Er ions have an intense
ESA effect on the light source of approximately 800 nm, so that the
light source of 800 nm is used to excite the Er ions at the
meta-stable state 4I.sub.13/2 to the 2H.sub.11/2 energy level. In
other words, by utilizing the technique of doping both Er and Yb
and the double pumping light sources, the entire green light laser
efficiency of the optical fiber doped with Er is improved.
In the above mechanism, the optical fiber doped with both Er and Yb
serves as the basis. However, if the optical fiber is merely doped
with Er, the green light effect can also be generated. Based on the
above mechanism of utilizing various light sources with the low
energy to excite for several times to reach the green light energy
level, the adopted light sources are not limited to double pumping
light sources. Considering the energy level of the Er ions, a light
source of approximately 1480 nm, for example, may be further
utilized for compensation, so as to improve the efficiency.
The present invention is described as follows with several
embodiments, but the present invention is not limited to the
embodiments. The following embodiments can be appropriately
combined to one another.
The technical solution is achieved by the following method and
materials, for example, a pumping technique with a plurality of
light sources and a pulse modulation technique for pumping light
sources are adopted, and a fluoride optical fiber doped with both
Er and Yb is taken as an example, in which Yb element is used for
auxiliary effects, so it is not absolutely necessary. The theory
background of the exciting mechanism is described as follows.
The pumping technique with a plurality of light sources is adopted
considering a valence electron configuration of .sup.4f.sub.11 of
the Er ion Er.sup.3+, which has a .sup.4I.sub.15/2 ground state and
includes .sup.4I.sub.13/2, .sup.4I.sub.11/2, .sup.4I.sub.9/2,
.sup.4F.sub.9/2, .sup.4S.sub.3/2, .sup.2H.sub.11/2,
.sup.4F.sub.7/2, .sup.2H.sub.9/2, and other low level excited
states. FIG. 1 shows an absorption spectrum of an Er ion according
to an embodiment of the present invention, and FIG. 2 shows a
valence electron configuration of an Er ion according to an
embodiment of the present invention.
Referring to FIG. 2, the Er ion has been widely applied to the
laser of 1550 nm, and furthermore, the Er ion Er.sup.3+ further has
a green light laser transition mechanism, for example,
.sup.4S.sub.3/2.fwdarw..sup.4I.sub.15/2. In a silicon-based optical
fiber, the laser wavelength is in a range from 540 nm to 550 nm.
Various different pumping light sources may be adopted to excite
the ground state Er ion to .sup.4S.sub.3/2. Referring to FIG. 1,
although the Er ion has several absorption wave bands, only the
diode lasers using the pumping light source in the infrared wave
band, for example, 800 nm, 970 nm, and 1480 nm can achieve economic
benefits. However, the pumping light source cannot directly excite
the Er ion to the .sup.4S.sub.3/2 energy level to generate the
required green light of approximately 540 nm.
FIG. 3 is a schematic view of an excitation performed on an Er ion
by a pumping light source of 800 nm according to an embodiment of
the present invention. Referring to FIG. 3, if only the pumping
light source of 800 nm is used, the Er ion must repeatedly absorb
two photons, so as to reach the energy level for emitting the green
light. FIG. 4 is a schematic view of an excitation performed on an
Er ion by a pumping light source of 970 nm according to an
embodiment of the present invention. Referring to FIG. 4, if only
the pumping light source of 970 nm is used, the Er ion also must
repeatedly absorb two photons, and then emits the green light from
the .sup.4S.sub.3/2 energy level. FIG. 5 is a schematic view of an
excitation performed on an Er ion by a pumping light source of 1480
nm according to an embodiment of the present invention. Referring
to FIG. 5, if only the light source of 1480 nm is used, the Er ion
must repeatedly absorb three photons.
However, if the light sources of the above three wave bands are
separately used, they are still physically limited, thereby
affecting the conversion efficiency. As seen from the manner of
FIG. 4, in an energy level up-conversion mechanism of the Er ion
using the light source of 970 nm, the Er ion in the
.sup.4I.sub.15/2 ground state absorbs the photon of 970 nm and is
transited to the .sup.4I.sub.11/2 excited state, then absorbs the
photon of 970 nm and is transited to the .sup.4F.sub.7/2 excited
state, which must be accumulated to the population of the Er ion in
the .sup.4I.sub.11/2 excited state. However, the .sup.4I.sub.11/2
excited state may be relaxed and transited to a .sup.4I.sub.13/2
meta-stable state in a non radiation manner, in which the life
cycle of .sup.4I.sub.13/2 is longer than that of .sup.4I.sub.11/2,
such that the population of the Er ion is accumulated at the
.sup.4I.sub.13/2 meta-stable state instead of the .sup.4I.sub.11/2
excited state. As a result, the efficiency of the energy level
up-conversion mechanism of the Er ion using the light source of 970
nm to .sup.4S.sub.3/2 is restricted.
Furthermore, as for the mechanism of using the light source of 800
nm, as shown in FIG. 3, the Er ion in the .sup.4I.sub.15/2 ground
state absorbs the photon of 800 nm and is transited to the
.sup.4I.sub.9/2 excited state, then is relaxed and transited to the
.sup.4I.sub.13/2 meta-stable state, and then further absorbs the
photon of 800 nm and is transited to .sup.2H.sub.11/2. Referring to
FIG. 6, it shows an ESA rate of an Er ion according to an
embodiment of the present invention. As known from FIG. 3, the Er
ion in the .sup.4I.sub.13/2 state needs to absorb a photon with a
wavelength of 800 nm. However, as shown in the data of FIG. 6, the
GSA of the Er ion on the photon of 800 nm is rather poor. In this
manner, the efficiency of generating the green light only by using
the photon of 800 nm is not desirable.
Furthermore, the absorption spectrum of the Er ion shown in FIG. 1
is inspected again, in which an absorption section of the Er ion at
1480 nm is much larger than that of 800 nm and 970 nm. However, in
order to use the 1480 nm, twice energy level up-conversion
processes are required to transit to .sup.4F.sub.7/2, such that the
total efficiency is not high.
Therefore, the practical solution is, for example, using three
types of pumping light sources at the same time, so as to increase
the probability of the up-conversion to .sup.4S.sub.3/2.
Considering the main up-conversion path thereof, the light sources
of 970 nm and 1480 nm are used to accumulate the population in the
.sup.4I.sub.13/2 meta-stable state, then the Er ion absorbs the
photon of 800 nm and is transited to the .sup.4I.sub.9/2 excited
state, and then is relaxed and transited to the .sup.4S.sub.3/2, so
as to form a green light laser mechanism. The absorption section of
the light source of 1480 nm is fairly large, and the quantum
conversion efficiency is quite high. In other words, the Er ion is
excited by using the light source of 970 nm, so as to improve the
population in the .sup.4I.sub.13/2 meta-stable state. Then, the 800
nm photon is absorbed, so that the Er ion is transited from the
.sup.4I.sub.13/2 meta-stable state to the .sup.2H.sub.11/2, and is
then relaxed and transited to the .sup.4S.sub.3/2, so as to emit
the green light.
The above mechanism is directed to the optical fiber merely doped
with Er ions. However, since the adopted light sources include the
light source of 970 nm, the optical fiber may also be doped with Yb
ions. The function of using the light source of 970 nm further
includes impelling the Yb ions in the optical fiber doped with both
Er and Yb ions to be converted into the Er ions through the strong
absorption effect of the Yb ions on the photons of 970 nm, thereby
improving the efficiency. FIG. 7 is a schematic view of an energy
conversion between Er ions and Yb ions according to an embodiment
of the present invention. Referring to FIG. 7, when the Yb ion also
absorbs the light source of 970 nm, the Yb ion has a high GSA on
the light source of 970 nm, so that the Yb ion is transited from
the .sup.2F.sub.7/2 ground state to the .sup.2F.sub.5/2 excited
state. When the Yb ion is transited back to the .sup.2F.sub.7/2
ground state from the .sup.2F.sub.5/2 excited state, the emitted
photon is absorbed by the neighboring Er ion, thereby improving the
efficiency for absorbing the light source of 970 nm by the Er
ion.
Then, the function of a pulse pump is described. FIG. 8 is a
schematic view of a frequency up-conversion efficiency simulation
by using a Monte Carlo algorithm according to an embodiment of the
present invention. Referring to FIG. 8, three fitting curves are
obtained by simulating the relation between the photo population
inversion and the up-conversion efficiency (also called frequency
up-conversion efficiency) in different unit times. It is shown from
the data that, the high population inversion improves the laser
up-conversion efficiency. Therefore, a short pulse time width may
be used, and a full width at half maximum (FWHM) is at the nano
second level. Through a high power laser, the Er ion is transiently
excited to the energy level in the pulse time, thereby improving
the up-conversion efficiency.
As for a fluoride optical fiber, the life cycle of the electron on
the energy level is relevant to the material of the optical fiber.
When the Er ion is respectively doped in optical fibers of ZBLAN
and silica, the life cycle of the high excited state
.sup.4F.sub.7/2 in the optical fiber of ZBLAN is 0.45 ms, and the
life cycle of the energy level in the optical fiber of silica is
only 0.001 ms or 1 .mu.s, which can be explained by a multi-phonon
emission. As for a certain energy level, the speed W of the
multi-phonon emission can be represented as a function of an energy
difference .DELTA.E between the current energy level and the next
energy level, that is,
.times..times..function..DELTA..times..times..times..times..omega.
##EQU00001##
In the above equation, C and a are constants, and h.omega. is a
phonon energy of the material, which is approximately 1000
cm.sup.-1 or 124 meV in the material of silica and Borate glass. In
ZBLAN, the value h.omega. is smaller than 600 cm.sup.-1 or 74.4
meV, and is approximately a half of the former value. The
difference caused by the half value is extremely large in terms of
the index. The emission speeds of the .sup.4S.sub.3/2 energy level
of the Er ion are quite different in Borate glass, silica glass,
ZBLAN, and LaF.sub.3, which is approximately 4.5*10.sup.5 S.sup.-1
in silica, and is approximately 10.sup.3 in ZBLAN, which indicates
that the life cycle difference there-between is approximately 450
times.
Furthermore, the absorption spectrum of the Er ion on the light
source of 1480 nm in optical fibers of different materials is
analyzed as follows. The ZBLAN material has smaller phonon energy,
which does not easily affect the life cycle of the Er ion at the
high energy level, and thus the optical fiber of ZBLAN is suitable
for serving as a host for a frequency up-conversion laser. In the
frequency up-conversion, it is considered to further add the
pumping light of 1480 nm, through being transited from
.sup.4I.sub.15/2 to .sup.4I.sub.13/2, the ion quantity at the
energy level .sup.4I.sub.13/2 is improved, so as to prevent the
ions at .sup.4I.sub.11/2 from being relaxed to the energy level
.sup.4I.sub.13/2 due to the life cycle of the energy level as short
as 7 .mu.s. The absorption sections of the Er ion doped in several
different materials are inspected. The absorption of the ZBLAN in
the light source of 1480 nm is higher than that of the silica.
Therefore, the optical fiber of ZBLAN is preferred considering the
life cycle in the high level and the absorption at the light source
of 1480 nm.
Several phenomena may be concluded from the above research. If the
light sources in the three wave bands are used separately, they are
somewhat limited physically, thereby affecting the conversion
efficiency. That is to say, for the light source of 800 nm, the GSA
of the Er ion is rather poor. For the light source of 970 nm, the
probability of the Er ions at .sup.4I.sub.11/2 is low, the
population thereof is low, and it is difficult to absorb the
pumping light source. For the light source of 1460 nm, the Er ion
must repeatedly absorb three photons at the same time, so that the
efficiency is poor.
Therefore, the practical solution is, for example, using three
types of pumping light sources at the same time, so as to increase
the up-conversion probability to .sup.4S.sub.3/2. Considering the
main up-conversion path, the light sources of 970 nm and 1480 nm
are used to accumulate the population in the .sup.4I.sub.13/2
meta-stable state, then the photon of 800 nm is absorbed, and then
the ions are transited to the .sup.4H.sub.11/2 excited state and
then relaxed and transited to .sup.4S.sub.3/2, so as to form a
green light laser mechanism.
Furthermore, the light source of 970 nm is used, such that the Yb
ion is further doped, so as to improve the efficiency for absorbing
the light source of 970 nm.
However, based on the multi-light source mechanism, the present
invention is not limited to the green light laser. In addition, the
ions doped in the optical fiber are considered according to the
excited state thereof, so that the types of the doped ions and the
number of the ion types are not limited.
The laser structure is described as follows. FIGS. 9-11 are
schematic views of a laser system according to several embodiments
of the present invention. Referring to FIG. 9, a combiner 100 is
disposed on an input end of an optical fiber 102, such that a
plurality of pumping light sources is introduced to the optical
fiber 102 through the combiner 100. The pumping light sources
include at least two light sources, for example, a pumping light
source 108 and a pumping light source 110. For a green light laser,
the optical fiber 102 is doped with Er ions or is further doped
with Yb ions. The wavelengths of the pumping light source 108 and
the pumping light source 110 are, for example, from 790 nm to 825
nm and from 960 nm to 990 nm. According to the practical needs, a
pumping light source 112 is further added, and the wavelength
thereof is in a range of, for example, from 1450 nm to 1550 nm.
Furthermore, a pumping light source from 900 nm to 930 nm, for
example, may be added as well. Two optical-fiber gratings 104 and
106, for example, fiber Bragg gratings (FBGs), are disposed on two
ends of the optical fiber 102, so as to form a resonance cavity. A
central wavelength of the optical-fiber gratings is, for example, a
green light of approximately 546 nm.
Referring to FIG. 10, it is similar to FIG. 9, except that the
optical fiber 102 is not configured with the optical-fiber gratings
to form the linear resonance cavity. The green light laser is
introduced to the optical fiber 102 through a seed light source 113
with the wavelength of 540 nm and through the combiner 100. As the
green light seed light source 113 is added, it is not necessary to
dispose the green light optical-fiber gratings on the optical fiber
102 to form the resonance cavity.
Referring to FIG. 11, the laser system forms an annular resonance
cavity by using an annular optical fiber 102. The pumping light
sources 108, 110, and 112 are introduced to the optical fiber 102
through the combiner 100. An optical coupler 120 is disposed on the
optical fiber 102, so as to output a required laser light 124,
which is a green light with a wavelength of, for example, 540 nm.
In addition, an isolator 122 directionally for the green light is
also disposed on the optical fiber 102.
In a laser system, the above mentioned mechanism is utilized, a
plurality of light sources with the low energy is used, and the
ionization properties of the doped ions is utilized as well, so as
to achieve the laser light with the higher energy level through the
excitations for several times, for example, emitting a green
light.
It will be apparent to those skilled in the art that various
modifications and variations can be made to the structure of the
present invention without departing from the scope or spirit of the
invention. In view of the foregoing, it is intended that the
present invention cover modifications and variations of this
invention provided they fall within the scope of the following
claims and their equivalents.
* * * * *